<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>

<body>

    <!-- concat :用于两个或者多个数组
    该方法不会改变现有的数组,而是仅仅返回被连接的数组的一个副本 -->
    <div>
        <button class="btn btn-default" onclick="btn()">点击合并数组</button>
    </div>

    <script>
        var cn = ["cn1", "cn2", "cn3"];
        var bn = ["bn1", "bn2", "bn3"];
        var dn = cn.concat(bn);
        var Cn = document.getElementsByClassName(".btn");

        function btn() {
            alert(dn);
        }
    </script>
</body>

</html>